This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. All cells must traffic proteins across their membranes. This essential process is responsible for the biogenesis of membranes and cell walls, motility and nutrient scavenging and uptake, and is also involved in pathogenesis and symbiosis. The translocase is an impressively dynamic nanomachine that is the central component which catalyses transmembrane crossing. This complex, multi-stage reaction involves a cascade of inter- and intramolecular interactions that select, sort and target polypeptides to the membrane, and use energy to promote the movement of these polypeptides across--or their lateral escape and integration into--the phospholipid bilayer, with high fidelity and efficiency. SecA is a large 204 kDa motor protein of the Sec translocation machinery.